In the sole disclosed in FR-A-2 91 441, the edges of the blades of the lower chamber protrude above the lower plane of the peripheral shoulder, the thin sheet closing the lower chamber being, at rest, inflated in its central portion above the edges of the blades. On the other hand, the upper chamber is also provided with slanting blades the edge of which is independant of the deformable thin sheet or plate which closes said upper chamber, these blades being inclined in the reverse direction to those of the lower chamber.
In practice, it has proved that the fluid circulation in the upper chamber in contact with the sole of the foot, which circulation provides for the massage effect which is desired with this type of shoe sole, was broken by the blades provided in this chamber since said blades were stretched taut between the two sides of the peripheral shoulder and were bearing over their whole length against the thin closing sheet, which sheet is in turn stretched taut inside the frame formed by the shoulder. Moreover, the upper surface of the peripheral shoulder is connected to the plate forming the separation between the upper and lower chambers by a surface reached by the blades, which is perpendicular to said upper surface and to said plate. When the flexible sheet is being welded on the shoulder upper surface, the welding flows above the chamber and forms an enlargement of a few millimeters, thereby reducing the active surface of the shoe sole in contact with the sole of the foot, and proves unconfortable for the user. Moreover, when the peripheral shoulder of the thin sheet is being welded on the upper or lower narrow plane surface of the shoulder, it has proved difficult to obtain a safe tight welding.
In order to remedy the braking of the fluid circulation due to the action of the rigidity of the stretched blades, it has been imagined to make the side of the blades independent from the shoulder by forming a thin slot between the shoulder and the end thereof which is connected to the blade. However, the effect of this slot can be cancelled by a point of glue between the welding enlargement of the flexible sheet on the peripheral shoulder surface and the blade edge. If the independence of the blade with respect to the shoulder is maintained, the fluid follows a preferential passage of lesser resistance opposite the slot, thereby reducing the fluid circulation in the central portion where the contact with the sole of the foot is maximum.